Field desorption mass spectrometry of phospholipids. III. Survey of structural types

A survey has been conducted of the behavior of a wide variety of phospholipids and related materials under field desorption mass spectrometric conditions. Phosphatidyl cholines, both acyl and alkyl, phosphatidyl ethanolamies, phosphatidic acids, the corresponding lyso compounds, glycerophosphoryl lipids and sphingolipids are among the species studied. Most of the 50 compounds measured as single species gave M + H as base peak, some associated ions, and fragment ions which became increasingly significant at higher anode temperatures. Problems encountered include interference from organic impurities and alkali metal ions, poor reproducibility of minor ions due to low ion collection rates and potential confusion in structrual assignments caused by reactions occurring on the anode prior to desorption. Various approaches to overcome these difficulties are discussed, and the potential of the field desorption technique for species specific analysis of naturally occurring phsopholipid mixtures is demonstrated by three examples.